The present invention relates to electromagnetic interference suppression devices for RJ connectors. In particular, the present invention relates to RJ connectors which suppress electromagnetic interference at the bottom portion of the connector.
Networking and telecommunications equipment commonly use RJ connectors as the interface between the data terminal equipment and the unshielded twisted pair cables which carry the high-speed data signals. The high-speed digital signals entering and/or leaving the system by means of these connectors and their associated cables are prone to having Electromagnetic Interference (EMI) problems at the interface of the RJ connectors and the cable.
The printed circuit board (PCB) layout and system design of the networking and telecommunications equipment is critical to the functional and EMI performance of that system. There are many different techniques used by PCB and systems designers to combat EMI. However, many of the tried-and-true EMI suppression techniques were developed for a standard configuration where the line interface magnetics are separated from the RJ connectors.
A typical line interface configuration that is used in Ethernet and other networking equipment is where the PCB layout has separate ground planes that are specifically partitioned to keep different types of signals localized in distinct functional blocks. With this typical line interface configuration, there are several important factors which prevent EMI from being coupled onto the data transmission cables. One factor is that the RJ connector is placed on a ground plane that is electrically separated from the rest of the PCB and connected to the system chassis. This effectively creates a barrier that isolates the RJ connector from the noisy digital signal currents present on the PCB. Additionally, the chassis ground plane shields the RJ connector from the electromagnetic fields present on the PCB and inside the system enclosure.
While effectively suppressing EMI noise, such line interface configurations, however, have many disadvantages. These systems often require a large amount of PCB area, additional spacing for safety and hi-pot requirements, localized noise filtering and bypass, an increased magnitude and number of parasitic circuit elements, and a non-optimum component placement and special PCB track routing techniques.
With the rapid advances in technology bringing forth electronic circuits and systems that are smaller, faster and more complex, PCBs are becoming more densely packed, with virtually every square millimeter of board space being utilized. Hence, the PCB area required for bulky connectors and other hardware is becoming more critical, and systems designers are looking for ways to reduce the area consumed by such hardware.
One breakthrough in connector technology is an RJ connector with integrated magnetics, such as the BelMag™ product line from Bel Fuse, Inc. Many of the disadvantages of standard line interface configurations are alleviated with the use of RJ connectors with integrated magnetics. By combining the line interface magnetics and the RJ connector into a single housing, a substantial reduction in the required PCB area is realized. Moreover, the integrated connector provides significant improvements in the overall systems performance.
Accordingly, these RJ connectors with integrated magnetics are being deployed in networking and telecommunications systems as a means to reduce size, lower manufacturing costs, and improve system performance. However, even with all of the benefits provided by the use of such integrated connectors, some of the methods traditionally used by systems designers to control and reduce EMI emissions no longer apply. Hence, designing for EMI compliance is, to some extent, shifting from the PCB and systems designers towards the integrated connectors' ability to effectively filter or suppress the EMI emissions, particularly at the high end of the EMI spectrum. Because of this, there are other EMI issues associated with the use of integrated RJ connectors that need to be addressed.
For example, since the magnetics are located inside the RJ connector, the system's PCB layout will be entirely different. Separate islands of digital, analog and chassis ground planes may not be available to implement the EMI suppression techniques previously discussed. Hence, a system utilizing integrated connectors sometimes experience aperture leakage. Simply stated, this means that there is, in effect, a “hole” in the EMI shielding at the unshielded area on the bottom of the connector (where the pins of the connector are located). This, coupled with what amounts to small “antennas” formed by the pins and the conductors within the integrated connector, can result in high frequency noise escaping from the equipment enclosure and either radiating into the environment or being coupled onto the transmission cable connected to the integrated RJ connector.
Trying to solve the aperture leakage problem on a system level is not practical due to the vast number of variables involved. This is because different systems will have different circuit designs, physical and electrical properties, PCB layout, etc.
Accordingly, there remains a need for an integrated RJ connector which provides both electromagnetic and electrostatic shielding while shunting very high frequency noise on the signal lines to ground to thereby alleviate aperture leakage problems.